This invention relates generally to processing within a computing environment and more particularly to serializing requests in a multiprocessor system.
Multiprocessor systems can take a variety of forms and individual designs may contain many unique features. Common among multiprocessor systems is the requirement to resolve shared resource conflicts. Shared resource conflicts occur when more requestors attempt to access a shared resource than the resource can process at a given time. Resolving this type of conflict necessitates serialized access. As bandwidth between processors and caches is increasing at a faster rate than bandwidth between caches and memory, and an overall number of physical memory interfaces remains the same due to chip input/output constraints, physical memory is a shared resource that is more commonly experiencing access contention from many requestors. If requests for shared resources, such as memory, are not resolved fairly, requests may time-out or large variations in request service time may develop. Time-out and variations in request service time contribute to an overall degradation in system performance. As the number and speed of processors increase, efficient and equitable shared resource coordination is even more desirable.
Currently, shared resource coordination employs pre-priority filtering that holds requests for a processor in a pipeline until a targeted resource becomes available. A request is looped out of and back into the pipeline until the targeted resource is available. Pre-priority filtering relies on a central pipeline structure that employs rank priority at a final request group level to meet performance requirements of minimizing latency to local caches. Another existing approach to workload coordination employs a round-robin scheme. The round-robin scheme provides the pipeline with course-grain control over allocation of memory request slots.